Various embodiments are based on a circuit arrangement for operating discharge lamps. Many circuit arrangements for operating discharge lamps have a power factor correction circuit for converting the input voltage into a suitable DC voltage, which is often also regulated, said DC voltage being referred to as the intermediate circuit voltage and then being fed to the inverter. The power factor correction circuit, which is generally a step-up converter in terms of circuit topology, brings about a sinusoidal current consumption of the entire arrangement and at the same time a regulated intermediate circuit voltage of a suitable level. These circuit arrangements are incorporated in control gear for low-pressure or high-pressure discharge lamps and are generally fed by an AC system voltage. In the case of the power factor correction circuit as a step-up converter, the converter switch is arranged between the incoming and return current path of the circuit, i.e. is not directly in the main current path.
In order to keep the intermediate circuit voltage stable and in order to limit ripple currents, such circuit arrangements generally have a so-called intermediate circuit capacitor, which is connected between the two output terminals of the voltage converter or the power factor correction circuit or between the input terminals of the inverter and also acts as backup capacitance for the voltage converter. If the control gear is now switched on, i.e. the entire circuit arrangement is connected to the power supply system, the intermediate circuit capacitor, i.e. the backup capacitance of the step-up converter, is charged via the converter current path of the step-up converter in a very short period of time via the converter inductor and the boost diode, which results in a very high switch-on current, particularly when switching on happens to take place at the system peak. In the worst case scenario, the capacitor is charged over only one system cycle or even only one system half-cycle. In this case, the system peak is intended to mean the time of the (positive or negative) peak value of the system voltage. The current path via which the backup capacitance is charged is referred to below as the charging current path. The level of the switch-on current can be a multiple (measured up to 200×) of the rated operating current. As a result, the use is restricted to an overcurrent protection since the circuit breaker is triggered in the event of a plurality of devices being simultaneously switched on, although the maximum current of the circuit breaker has by far not yet been reached when the rated current of the devices is taken into consideration.
In order to limit the switch-on current, EP 067 18 67 A has therefore proposed a circuit arrangement which has a parallel circuit including a resistor and a thyristor in the current path of the converter. At the switch-on time of the circuit arrangement, the thyristor is off and only the resistor in the current path is active. The intermediate circuit capacitor is charged slowly and with a low current via said resistor. When the intermediate circuit capacitor has been charged to a predetermined voltage, the thyristor is turned on and bridges the resistor, with the result that the losses are kept low during operation. The circuit arrangement requires many additional component parts, however, and has the disadvantage of high power losses at the switch-on time since there is a power drop which should not be underestimated at the current-limiting resistor.